The invention relates to an electric lamp provided with:
a light-transmitting lamp vessel which is closed in a vacuumtight manner and in which an electric element is arranged connected to current conductors which issue to the exterior from the lamp vessel; PA1 a lamp cap which is securely connected to the lamp vessel and which has a housing of synthetic resin with an outwardly projecting collar and a base portion comprising openings through which the current conductors extend to contact members of the lamp cap, PA1 sealing means being present in the housing for sealing off the openings in the base portion around the current conductors.
Such an electric lamp is known from EP 0 129 868-B1. The lamp is suitable for use as a vehicle headlamp when mounted in a reflector. It is desirable in this application that moisture and pollutants cannot deposit in the reflector. The outwardly projecting collar is designed to abut against the reflector so as to limit the depth to which the lamp can be inserted through an opening in the reflector.
Sealing means are present in the known lamp for preventing moisture and pollutants entering the reflector along the current conductors through the lamp cap. After the lamp vessel has been aligned with its electric element relative to the lamp cap, the current conductors are fastened to the contact members in the known lamp. Then a quantity of sealing compound is brought into the lamp cap housing and this compound is made to solidify at a raised temperature during, for example, one hour. A liquid or powdery synthetic resin, for example epoxy resin, is used for this purpose.
A disadvantage of the construction of the known lamp is that the application and drying or curing of the compound is time-consuming and retards the production process. It is also necessary to prevent volatile components from the compound from being released during lamp operation. Another disadvantage is that only those materials can be used which adhere both to the lamp cap and to the current conductors. A further disadvantage is that the sealing compound could pollute the lamp, for example, the lamp vessel.
The lamp cap of the known lamp is a linear one, i.e. the contact members lie in the extended direction of the lamp vessel.
EP 0 172 529-B1 discloses another lamp designed for use in a reflector where the lamp cap has collars around the respective openings in the base portion, which collars are fused to the current conductors after these current conductors have been passed through. A disadvantage of this is that an additional operation is necessary for obtaining a seal. Another disadvantage is the risk that the seal is not permanent owing to the differences in coefficient of thermal expansion between the synthetic resin and the current conductors.
The lamp cap of this lamp is a transverse one, i.e. the contact members extend transverse to the extension of the lamp vessel.
EP 0 193 997-B1 discloses a similar electric lamp in which the space behind the base portion of the lamp cap is filled with a synthetic resin so as to seal off the housing of the lamp cap. However, volatile components could escape from this synthetic resin. The lamp vessel is secured in the lamp cap by means of a metal clamping plate which grips the lamp vessel with clamping force and a metal cylinder which is mounted in the lamp cap and which is welded to the clamping plate. The metal cylinder is fixed by means of twisted tongues which project through the base wall.